Familial aggregation of the Type A behavior pattern, its components and standard risk factors for coronary heart disease (total cholesterol and trigylcerides, HDL-C and LDL-C, systolic and diastolic blood pressure and relative weight) will be investigated. The sample for this epidemiologic study will consist of 275 twin pairs, six to eleven years old, and their parents. Genetic and environmental sources of variation will be ascertained by comparing monozygotic pairs with same-sex dizygotic pairs. Opposite-sex twins will be analyzed as matched pairs to examine sex differences in the Type A behavior pattern among children. It will be determine whether or not the Type A behavior pattern or its components is correlated with any of the standard risk factors in this pediatric population. Familial aggregation of these characteristics will be studied using data on the twins and their parents. It is important to identify the extent to which the Type A behavior pattern in children can be attributed to genetic factors. Once this has been accomplished it will be necessary to determine the specific environmental factors that interact with the propensity to develop this risk factor. It is anticipated that the results of this study will provide insight into the origins of the Type A behavior pattern.